We have Isaac Newton to thank for a lot of things because of his prodigious studies and contributions to the body of scientific understanding. Among those things are the labels that we use for the visible spectrum. In the 17th century, Newton’s experiments with optical prisms yielded the first on-demand rainbows, if you will, in the history of scientific inquiry.

Curiously, despite his genius and sharp observational skills, Newton was quite terrible at distinguishing colors. In his original experiments, he identified the components of the visible spectrum as red, yellow, green, blue, and violet—merely five colors. Later, however, he revised his work on the visible spectrum and expanded the spectrum to include the additional colors of orange (between red and yellow) and indigo (between blue and violet). The change was driven primarily by Newton’s belief that seven was significant in the natural world as there were (then) seven known bodies in the solar system, seven notes in a musical scale, and seven days in the week.

It would be interesting, to say the least, if the world was different and he was firm in the belief that eight or nine was the number of true significance. Would we have an additional color in the spectrum? Perhaps teal (around 490 nm wavelength in the visible spectrum) or azure (around 435 nm)?